Evaluation of the image quality and exposure to radiation in different cephalometric techniques
Drs. J.A.C. Bottrel, H.A. Koch, L.G. Araújo, B.N. Bottrel, and E.N. Bottrel compare conventional, scanned, and digital radiographs for image quality and radiation exposure
Educational aims and objectivesThis article reports the results of a study conducted to compare variations in the methods of obtaining radiographic images among the conventional, scanned, and digital types, and the resulting disparity in the visualization of anatomic structures, interpretation and measurement errors, and the potential this has to compromise orthodontic or orthosurgical treatment.Expected outcomesCorrectly answering the quiz questions following the article, worth 2 hours of CE, will demonstrate the reader can:• discuss the effect that variations in the methods of obtaining radiographic images has on visualization of anatomic structures, interpreting data, and orthodontic treatment.• list the cephalometric structure points studied.• describe the effects of errors in patient positioning and exposure factors.
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Cephalometric radiography has a fundamental role in the diagnosis and planning of dentofacial deformation. Variation in the methods of obtaining radiographic images among the conventional, scanned, and digital types can lead to alterations in the visualization of anatomic structures, inducing interpretation and measurement errors, and thereby increasing the potential to compromise orthodontic or orthosurgical treatment. In Brazil, the great majority of radiologic services entail cephalometric radiography of the conventional type. This article analyzes comparatively the quality of images of 16 points and cephalometric structures derived from radiographs of 15 adults, obtained through conventional, scanned, and digital techniques. Errors in the positioning of the patient and the exposure factors used were also evaluated between the conventional and digital types.
From a Likert scale of image classification, three evaluators established concepts for each one of the 16 selected cephalometric points, obtaining the average of these scores through radiography type. The results demonstrated that, in relation to the 16 cephalometric points observed, the highest average of visualization quality was found in the conventional radiography group (1.63), followed by the digital group (1.45); the lowest was the scanned group (0.90). The intraclass correlation coefficient showed a reasonable concordance (ICC=0.446) between the three types analyzed, with the Friedman test being significant (p-value < 0.001). When the positioning of the patient and exposure factors in conventional and digital radiographies were evaluated, the highest average was also observed in the conventional radiography group (1.50), and in the digital group (1.01), low concordance (ICC=0.162), confirmed by p-value (0.002), was observed. During realization of conventional and digital radiographies, thermoluminescent dosimeters TLD100H Bicron STI/Harshaw were placed on the skin of the right genian region of the participants to evaluate the exposure to radiation. It was verified that the value of kerma in the air on the surface of the skin during digital radiography is more than 10 times lower than during conventional radiography, which is a great advantage of digital radiography. IntroductionLateral cephalometric radiography is the result of a radiographic method also known as teleradiography, in which the focal distance is approximately 1.50 meters, and the incident beam is parallel to the patient’s face, allowing us to analyze the craniofacial complex structures.
In cephalometry, it is necessary to identify anatomic points that should be fixed and representative of the determined structure to be analyzed, and that allow the construction of planes and lines that enable the measurement of certain cranial structures.
The certainty in the identification of a cephalometric point depends on the quality of the cephalogram, on the overlapping degree of the neighboring structures, on the knowledge of radiographic anatomy, and on the ability of the person who performs the cephalometric tracing. The first digital system for intraoral radiographs was launched in the late 1980s, and now is used with relative frequency. Nevertheless, the use of digital extraoral radiography in dental offices is extremely limited, in part due to the high cost of the equipment. There are two types of digital radiography systems: “CCD” (charge-coupled device), and “SP” (storage of phosphorus). With the CCD system, the image is captured by a sensor connected to the computer, and shown on the monitor screen. In the SP system, a plate coated with phosphorus, comparable in size and thickness to radiographic film, replaces this, and the intensifying grids in a film chassis are exposed to x-rays in the traditional way. The plate is then scanned, and the information is sent to the computer. The plate can be reused if exposed to a strong light source. These two systems are referred to as “direct digital images” (without film). An indirect digital image can be obtained by scanning a radiographic film exposed to radiation into the computer. Material and methodsIn this study, 30 lateral head cephalometric radiographs of 15 adults (7 female and 8 male) ranging in age from 18 to 50 years were used. Fifteen were obtained in the conventional way using a Gendex GX (Dentsply-Gendex), calibrated to 90 kV, 10 microampere (mA), and 0.8 seconds (s). An additional 15 radiographs were obtained digitally (CCD) using the Orthophos XG Plus (Sirona Dental Systems), calibrated to 90 kV and 12 mA, and stored on a CD. The 15 conventional radiographs were scanned later with an indirect digital system (Scanjet 4C/T; HP) using Adobe® Photoshop® (Adobe Systems) to create tif formats and then converting them to jpegs for storage on a CD. A total of 45 cephalometric images were taken.
Three evaluators, two orthodontists and one radiologist, gave grades relative to the quality of image of the 16 points and cephalometric structures frequently used, according to the Likert scale, widely used in the scientific environment, ranking the quality of images from very bad (-2), to bad (-1), to regular (0), good (1), and very good (2). This evaluation was made using the same illuminator for the analysis of the conventional film and only one monitor, with resolution of 1280 × 1024 pixels, for the visualization of digital and scanned images.
The cephalometric points and structures selected for this study were: 1. More projected upper and lower permanent central incisors 2. Permanent upper and lower left first molars 3. Point S (geometric center of sella turcica)4. Point N (junction of nasal and frontal bones)5. Porion point (most superior point of external acoustic meatus)6. Orbital point (inferior contour of the left orbit)7. Zygomatic process of the maxilla (key ridge)8. Pterygomaxillary breach (Ptm)9. Anterior nasal spine10. Posterior nasal spine11. Point A (premaxilla anterior contour)12. Point B (anterior contour of the menton symphyses)13. Mandible14. Pogonium point (most anterior point of menton symphyses)15. Condylar process16. Soft tissue profile.
Errors in taking the radiographs, such as the positioning of the patient in the cephalostat and the exposure factors, which determine the radiographs’ contrast and clearness, were also analyzed by the evaluators.
Thermoluminescent dosimeters (TLD100H, Bicron STI/Harshaw) in chip format, encapsulated in plastic packaging, were positioned on the patients’ right genian regions to evaluate radiation exposure while the conventional and digital radiographs were taken. Each package contained three TLD100H, which were obtained from the Thermoluminescence Dosimeter Laboratory, External Individual Monitoring Service of the Dosimetry and Radioprotection Institute, where they were analyzed.Statistical analysisThe statistical analysis consisted of average scores characterized by classical descriptive statistics (mean, standard deviation, minimum, maximum), and the concordance between these for the three radiographs was evaluated by the Intraclass Correlation Coefficient (ICC) and by the statistic tests of Friedman and Wilcoxon (in 2 by 2 comparisons).ResultsThe results obtained are displayed in Tables 1-5 and Figure 1, and analyzed in the discussion section.DiscussionThe purpose of this research was to comparatively analyze the quality of image of the same individuals through three different cephalometric techniques, allowing the elimination of fundamental differences, such as bone density and soft tissue contour, when groups of individuals had the same common characteristics, such as malocclusion or age.
The quality of the image of the 16 points and cephalometric structures selected for the present study, according to the analysis of three observers, was superior in the conventional radiography group, followed by the digital and the scanned group, respectively. This result agrees in part with the research of Demura et al,1 which evaluated visual and physical characteristics of the conventional and digital radiographs of 10 orthodontic patients, concluding that, in the visual test, digital radiography seemed much better than conventional radiography, enabling the identification of the cephalometric points more precisely. On the other hand, the physical characteristics and granulation of the conventional radiography were better. According to the authors, however, granulation and resolution are not strongly related to the identification of the cephalometric points, justifying the routine use of digital radiography. In a wider study, Bruntz et al2 compared the distortion, a measurement of the precision, and results of overlapping of the pre- and post-treatment radiographs of 30 patients among the digital (phosphorous storage), conventional, and scanned radiographs. The authors reported that although some distortion could be found in the scanned radiography, these were considered clinically insignificant.
In relation to the errors in the identification of the points in the scanned images, these contributed to the discrepancies in the cephalometric analysis when compared with the manual tracing of the conventional radiography. The overlapping performed by computer software in the scanned radiographs, however, was more precise than the overlapping done by manual techniques with conventional radiographs.
The investigation of the differences in the identification of the cephalometric points in human skulls in conventional and digital radiographs led Schulze et al7 to state that the results were very similar in relation to their precision and reproducibility having, however, increased benefits for digital images. On the other hand, the authors highlight the reduction of radiation and operational costs of the digital radiographies, in addition to the quick processing of data.
Yet, in relation to the cephalometric image quality aspect, Forsyth et al3 highlight that there are many potential benefits in producing digital images, including decrease of exposure to radiation, storage of the image, its manipulation and transmission, and the automated or semi-automated cephalometric analysis; however, all these advantages can be set aside if the diagnosis quality of conventional radiography cannot be outdone. The authors based their arguments mainly on the fact that the spatial resolution (capacity to register separate images of small objects that are extremely close) of the digitalized radiograph is smaller than that of the conventional radiograph. The smallest detail that is detected by human eye is 0.1 × 0.1 mm2, making it necessary for the pixels in digitalized images to be 0.1 mm in order to provide details comparable to conventional radiographies.
Wenzel and Gotfredsen8 evaluated nine digital systems for extraoral radiography and stated that there is no consensus about the degree of spatial resolution necessary for panoramic and cephalometric radiographies. The authors point out that CCD systems supply higher spatial resolution than SP systems, and this would lead to more clarity of details.
Conventional radiographs have a great advantage in relation to digital ones when it comes to image overlapping to evaluate growth or changes as a consequence of orthodontical treatment. Conventional radiography image augmentation can be easily controlled, while in digital radiography we are not sure if the size of the image is the same from one exposure to another. Ross and Munn5 recommend several procedures available in Adobe® Photoshop® to supplement any deficiencies of this digital technique. In relation to this important aspect, the standard prescription, according to Cohen,6 is having the distance from the x-ray source to the patient’s face 152.4 cm and the distance of the patient’s head from the film plate 15 cm, which allows for a precise method of comparison of the facial structures. The author states that in theory, any cephalostat that uses the standard distances increases the lateral cephalometric radiograph by 9.8%, and when this is compared to a digital radiograph, it will need alterations in the digital image, such as available when using Adobe® Photoshop®; however, in a different way from the one suggested by Ross and Munn.5
In this research, when patient positioning errors and exposure factors were analyzed, conventional radiographs were demonstrated to have a greater advantage in relation to digital radiographs (ICC=0.146), making it important to stress that both the conventional and digital images were obtained with the patients in a standing position, thereby taking natural head posture position into consideration. The postural position of the head has been proposed as the basis for the craniofacial morphological analysis by several authors11-15 in both the orthodontic and anthropological literature. In relation to this aspect, Yoon et al10 tried to identify potential errors of projection in the lateral cephalometric radiographs of 17 dry human skulls due to head rotation in vertical direction. The authors concluded that angular measurements presented fewer projection errors than linear measurements. Leitão and Nanda16 considered the Frankfurt plane and the palatal plane as good indicators of horizontal relation; however, the cephalometric vertical variables used to establish the sagittal position of maxilla and mandible, which are relatively precise in the maxilla but have great dispersion in the mandible, made the authors question their validity in detecting skeletal problems.
In terms of radiation exposure, it is uncontestable that there is a decrease in the radiation dosage in digital radiography as compared to conventional radiography. This research makes it evident that there is a reduction by a factor higher than 10. While in conventional radiography, values of kerma measured in the air on the surface of entrance in the right genian region vary from 53 to 126 µGy, in the digital radiography group, the highest value found was 5 µGy. This advantage of the digital radiography is described in all of the studies evaluated.3,17-22ConclusionsBased on the results presented, we can conclude that:1. In relation to the image quality and identification of the cephalometric points, conventional radiography was shown to be more efficient, with digital radiography very close in efficiency. The scanned radiographs, however, presented a notably inferior difference in image quality.2. When errors, such as patient positioning in the cephalostat and exposure factors were evaluated, the conventional image showed a significant difference compared with the digital.3. The radiation doses absorbed by the patients were drastically reduced in digital radiography.4. Considering the small difference in image quality between conventional and digital radiography, and the fact that radiation doses were extremely higher in conventional radiography, the routine use of digital radiography is recommended.
José Alexandre Bottrel, DDS, is Chair of the Brazilian Air Force Residence in Orthodontics in Rio de Janeiro, Brazil. He can be reached at
Hilton A. Koch, MD, MS, PHD, is Chair of Medical Radiology Department of the UFRJ.
Lídia G. Araújo, DDS, MS, is a full Professor in the Orthodontic Department of UFF.
Bruna N. Bottrel, DDS, MS, is Associate Dentist of the Brazilian Air Force Orthodontic Department.
Eduardo N. Bottrel, DDS, is a Resident in Oral Surgery at UFRJ.
References1.Demura N, Tsurusako Y, Segami N (2001) Characteristics of digital cephalograms and film/screen cephalograms: a comparative study. World J Ortho 2:350-355.2. Bruntz LQ, Palomo JM, Baden S, et al (2006) A comparison of scanned lateral cephalograms with corresponding original radiographs. Am J Orthod Dentofacial Orthop 130(3):340-348.3. Forsyth DB, Shaw WC, Richmond S (1996) Digital imaging of cephalometric radiography, part 1: advantages and limitations of digital imaging. Angle Orthod 66(1):37-42.4. Forsyth DB, Shaw WC, Richmond S (1996) Digital imaging of cephalometric radiographs, part 2: image quality. Angle Orthod 66(1):43-50.5. Ross LL, Munn MR (2005) Comparing digital serial cephalogram images for growth or treatment changes. Am J Orthod Dentofacial Orthop 128(2):161-162.6. Cohen JM (2005) Comparing digital and conventional cephalometric radiographs. Am J Orthod Dentofacial Orthop 128(2):157-160.7. Schulze RKW, Gloede MB, Doll GM (2002) Landmark identification on direct digital versus film-based cephalometric radiographs: a human skull study. Am J Orthod Dentofacial Orthop 122(6):635-642.8. Wenzel A, Gotfredsen E (2002) Digital radiography for the orthodontist. Am J Orthod Dentofacial Orthop 121(2):231-235.9. Benediktsdottir IS, Wenzel A, Petersen JK, et al (2001) Image quality in storage phosphor and CCD-based digital panoramic systems (abstract). Proceedings of the 13th International Congress of Dentomaxillofacial Radiology; 2001; Glasgow, UK. 10. Yoon Y, Kim K, Hwang M, et al (2001) Effect of head rotation on lateral cephalometric radiographs. Angle Orthod 71(5):396-403.11. Lundstrom, A (1982) Head posture in relation to slope of the sella nasion line. Angle Orthod 52(1):79-82.12. Lundstrom F, Lundstrom A (1992) Natural head position as a basis for cephalometric analysis. Am J Orthod Dentofacial Orthop 101(3):244-247.13. Moorrees CF, Kean MR (1958) Natural head position: a basic consideration in the interpretation of cephalometric radiographs. Am J Phys Anthropol 16:213-234.14. Cooke MS (1986) Cephalometric analysis based on natural head posture of Chinese children in Hong Kong (PhD Thesis) Hong Kong University of Hong Kong. 15. Viazis AD (1991) A cephalometric analysis based on natural head position. J Clin Orthod 25:172-182. 16. Leitao P, Nanda RS (2000) Relationship of natural head position to craniofacial morphology. Am J Orthod Dentofacial Orthop 117(4):406-417.17. Visser H, Rödig T, Hermann KP (2001) Dose reduction by direct-digital cephalometric radiography. Angle Orthod 71(3):159-163.18. Näslund EB, Kruger M, Petersson A, et al (1998) Analysis of low-dose digital lateral cephalometric radiographs. Dentomaxillofac Radiol 27:136-139.19. Visser HH, Hermann KP, Schorn C, et al (1997) Doses to critical organs from computed tomography. In: Farman AG, Ruprecht A, Gibbs SJ, et al, eds. Advances in maxillofacial imaging. Amsterdam, Netherlands:401-406.20. Tyndall DA (1989) Order of magnitude absorbed dose reductions in cephalometric radiography. Health Phys 56:91-95.21. Eliason S, Julin P, Richter S, et al (1984) Radiation absorbed doses in cephalography. Swed Dent J 8:21-27.22. White SC (1992) Assessment of radiation risk from dental radiography. Dentomaxillofac Radiol 21:18-126.
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